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Exam in 12 days

Exam in 12 days. in class assortment of question types including written answers. Read this article!. How does the visual system represent visual information?. Brainstorm this: what are the different ways the visual system might encode a feature?.

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Exam in 12 days

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  1. Exam in 12 days • in class • assortment of question types including written answers

  2. Read this article!

  3. How does the visual system represent visual information? • Brainstorm this: what are the different ways the visual system might encode a feature?

  4. How does the visual system represent visual information? • Brainstorm this: what are the different ways the visual system might encode a feature? • “labeled lines” • many different subnetworks of neurons - activity in a network indicates presence/nature of a feature • spike timing • absolute rate or # of spikes per second might indicate presence/nature of a feature • “multiplexed” • Hybrid of these two

  5. Visual Pathways • Themes to notice: • Contralateral nature of visual system • Information is organized: • According to spatial location • According to features and kinds of information

  6. Visual Pathways • Image is focused on the retina • Fovea is the centre of visual field • highest acuity • Peripheral retina receives periphery of visual field • lower acuity • sensitive under low light

  7. Visual Pathways • Retina has distinct layers

  8. Visual Pathways • Retina has distinct layers • Photoreceptors • Rods and cones respond to different wavelengths

  9. Visual Pathways • Retina has distinct layers • Amacrine and bipolar cells perform “early” processing • converging / diverging input from receptors • lateral inhibition leads to centre/surround receptive fields - first step in shaping “tuning properties” of higher-level neurons

  10. Visual Pathways • Retina has distinct layers • signals converge onto ganglion cells which send action potentials to the Lateral Geniculate Nucleus (LGN) • two kinds of ganglion cells: Magnocellular and Parvocellular • visual information is already being shunted through functionally distinct pathways as it is sent by ganglion cells

  11. Visual Pathways • visual hemifields project contralaterally • exception: bilateral representation of fovea! • Optic nerve splits at optic chiasm • about 90 % of fibers project to cortex via LGN • about 10 % project through supperior colliculus and pulvinar • but that’s still a lot of fibers! Note: this will be important when we talk about visuospatial attention

  12. Visual Pathways • Lateral Geniculate Nucleus maintains segregation: • of M and P cells • of left and right eyes P cells project to layers 3 - 6 M cells project to layers 1 and 2

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